The invention herein relates to devices for the application of adhesive, glue, that is, to one or more defined areas on a wrapping material, and in particular, on sheets or lengths of such material as are used for wrapping products of a prismatic shape, such as soaps, packs of cigarettes or similar articles packaged utilizing automatic wrapping machines.
In such machines, the sheets or lengths of wrapping material are conveyed in rapid succession to a wrapping station simultaneously with the single articles for packaging. During their progress toward the wrapping station, the sheets of material are provided with an adhesive at least along one side, and at one or more localized areas, which permits subsequently of fastening the wrappings formed by such sheets.
In prior art machines, the adhesive is contained in a tray or tank, and transfer of the adhesive to the sheet of wrapping material is performed by rotary components such as, for instance, channelled rollers, or coaxial disks (applicators) set apart one from the next to match the distance between centres of those localized areas on the sheet of wrapping material to which the adhesive must be applied.
Metering of the adhesive picked up by such rotary components in prior art machines is accomplished by fixed position scrapers.
These fixed position scrapers, clearly, are located upstream of the point where application of the adhesive to the sheet of wrapping material is brought about, and are generally contoured so as to breast with the front and lateral surfaces of those parts of the applicator disks that are in relief, in order to remove the adhesive substance from all such parts as might foul the sheet of wrapping material during application.
The match between the scraper and channelled roller (or applicator disks) must be particularly accurate in order to prevent the formation of voids, particularly near the corners, which would result in failure to remove a quantity of adhesive considerably in excess of that required, with the consequence that the following application of adhesive to the sheet of material may be marred by splashes or traces of glue falling outside the envisaged localized areas of the sheet.
It has been found in practice that considerable servicing is required in the prior art devices thus described in order to ensure efficient operation of the scrapers, particularly of their action against those lateral surfaces of parts of the channelled rollers or applicators that are in relief.
It happens frequently that, owing to wear or to the accumulation of encrustations which are not speedily removable, the scrapers must be replaced, and considerable amount of time is lost in adjusting them with respect to the parts to be wiped.
Devices of the type mentioned above have been seen to be suitable for the application of adhesive to sheets of wrapping material having a certain consistency, such as sheets of thin card, for example, though unsuitable for thin and flexible sheets of material such as those utilized for soft-packaging cigarettes (American wrappings). In this instance the sheet tends to crease at those points which remain unsupported during application of the adhesive, a situation which can give rise to faulty transfer of the adhesive, bringing with it the risk of runs into unwanted areas, and at all events of an excessive deposit of the adhesive along the side-edges of the localized areas of the sheet of wrapping material.
With the above in mind, it will be remembered that in order to receive the adhesive from the glue rollers or disks, the sheets of wrapping material are usually urged against such rollers and/or disks by contact rollers, which work in conjunction therewith.
It is the action thus produced which tends to give rise to the creasing aforementioned, especially in the case of sheets of extra-thin, hence extremely flexible material.
In other prior art systems, the rotary component that transfers adhesive from the tray or tank to the sheets of wrapping material consists of a roller the cladding of which incorporates pockets that are located according to the position of the localized areas of the sheet of wrapping material onto which the adhesive is to be transferred.
In order to keep the cladding of the roller clean, a fixed scraper is provided the function of which is to wipe the outer surface of the cladding, thoroughly, in such a way that adhesive picked up by the roller will remain in the pockets only.
During transfer of the adhesive from the glue roller to the wrapping material, a contact roller urges the sheet against the glue roller, (cleaned continuously by the scraper) such that at least a part of the adhesive contained in the pockets is transferred onto the sheet of wrapping material at the envisaged localized areas.
With this system, it becomes possible to dispense with the use of contoured scrapers such as are required for devices of the channelled roller or the side-by-side disk applicator type, and one has the advantage of being able to use a scraper having a practically linear edge which rests against the outer surface of the roller cladding and is easily adjustable in relation to this surface, providing optimum conditions of cleanliness at all times. What is more, the problem of creasing in the sheet of wrapping material is practically eliminated, since the entire width of the sheet rests against the outer surface of the roller cladding at the point where it is brought into contact. Nonetheless, when required to handle thin and extremely flexible sheets of material, it happens likewise in this instance that such devices are difficult to use in practice, and for a number of reasons.
The roller does not have circumferential channels; as a result there is no space available between the glue roller and the contact roller where guides can be located so as to take up the sheet of wrapping material exiting from the point at which the adhesive is applied. This poses no particular problem in the case of sheets of wrapping material having a certain consistency, since their own relative flexibility causes them to separate automatically from the glue roller and continue forward onto guides positioned downstream of the roller itself; for thin and highly flexible sheets of material however, devices of this type cannot be employed other than with great difficulty in terms of operation, due to the fact that the sheet of wrapping material exiting from the device tends to cling to the glue roller and thus follow a trajectory other than would be optimum. Such clinging is caused by a film of glue which remains on the outer surface of the roller, despite the action of the scraper.
This negative effect can occasion blockage of the device and cause the sheet to stick against the guides, so that shutdown of the machine is required in order to restore normal operating conditions.
The main object of the invention is that of providing a device for the application of adhesive to one or more localized areas of a flexible sheet of wrapping material, designed in such a way as to eliminate the disadvantages produced in similar prior art devices, and affording the possiblity of handling extremely flexible wrapping, with no risk whatever of the sheet of wrapping material clinging to the glue roller.
A further object of the invention is that of providing a device of the type in question, wherein the possibility exists of incorporating guides which take up the sheet as it exits from the device itself, located in such a way as to ride the outer surface of the glue roller in close proximity to the point where the adhesive is transferred from the glue roller to the sheet of wrapping material, and positioned so as to afford uninterrupted support to the exiting sheet without any risk of its sticking fast or becoming diverted from its path.